One of the interesting control mechanisms in cells of higher organisms is that involved in the regulation of the level of ribosomes in the cell. Such cells appear to regulate the concentration of ribosomes by altering the rate of synthesis of one or more of the components of the organelle, the rate of degradation, or both. It appears that in malignant cells there may be an alteration in the degradative aspect of the regulatory process. The long-range goal of this project is the elucidation of the process by which ribosomes are disposed of in non-malignant cells, the nature of the control of that process, and what alteration of the degradative system, if any, takes place in the malignant transformation of such cells by oncogenic viruses. The studies will be conducted using cells in culture to determine the degree of retention of ribosomal RNA which has been labeled by exposure of the cells to 3H-methyl methionine. Measurements will be made during growth and as growth slows due to population density inhibition. Similar determinations will also be made with cells transformed with oncogenic viruses in which the cell density at which growth slows is temperature sensitive. The biochemical events which accompany the shift from stability to turnover of the ribosomal RNA will be investigated.